The present invention relates to a semiconductor laser. More particularly, the present invention relates to a visual light semiconductor laser using a compound semiconductor material of AlGaInP.
The semiconductor laser using the compound semiconductor material, basically manufactured by laminated semiconductor layers having different compositions, requires steps of, except a step of semiconductor crystal layer growth, grasping etching or the like halfway although depending upon the shape thereof. Since the semiconductor wafer has to take out from a crystal growing furnace, the frequency of grasping the steps is better to be fewer in terms of productivity. Although it is general at present to take out the wafer twice halfway from the crystal growing furnace in the three continuous crystal growth steps, namely, before the uppermost semiconductor layer is completed in crystal growth, semiconductor lasers capable of being manufactured only with two steps of continuous crystal growing steps are disclosed in, for example, pages 1491 through 1496 (hereinafter referred to as document) IEEE Journal of Quantum Electronics) Volume 27, No. 6, July 1991 or in Japanese Unexamined Patent Publication No. 218993/1992. One of the representative semiconductor lasers in the above description are shown in FIG. 3 and FIG. 4.
FIG. 3 shows a semiconductor described in the document, where an n-type of AlGaInP clad layer 22, an n-type, a p-type or non-dope of GaInP active layer 23, a p-type of AlGaInP clad layer 24, and an n-type of GaAs current blocking layer 25 are laminated in order on an n-type of GaAs substrate 21.
Then, a stripe shaped groove reaching to the middle of the clad layer 24 through the current blocking layer 25 is formed, etching these layers. Further, a p-type of AlGaInP light guide layer 26, a p-type of AlGaInP clad layer 27, a p-type of InGaP layer 28, a p-type GaAs contact layer 29, and an AuZn/Au electrode 30 are laminated in order in the layer. AuGe/Au electrode 31 is provided on the reverse face to constitute the semiconductor laser.
Also, FIG. 4 shows another example of the conventional semiconductor laser described in the Japanese Unexamined Patent Publication No. 218993/1992. In the semiconductor laser described in FIG. 4, an n-type of AlGaInP clad layer 42, GaInP active layer 43, a p-type AlGaInP clad layer 44, a p-type of GaInP etching stop layer 45, a p-type of AlInP shutting in (or confining) layer 46, and an n-type GaAs current blocking layer 47 are laminated in order on an n-type GaAs substrate 41. Then, the current blocking layer 47 and the shutting in layer 46 are etched from the surface, forming a stripe shaped stripe groove reaching onto the surface of the etching stop layer 45. Further, a p-type of AlGaAs upper clad layer 48, a p-type of GaAs cap layer 49, and a Cr/Au electrode 50 are laminated in order. An Au/Ge/Ni electrode 51 is provided on the reverse face.
Such a conventional semiconductor laser has a problem in that the surface of the GaAs is deteriorated when the substrate temperature is raised under the atmosphere of PH.sub.3 gas at the next re-growing time in the use of GaAs or the like where an energy band gap is small having a light absorbing function as a current blocking layer so that the semiconductor crystal layer of the AlGaInP including P cannot be grown again in a good crystal condition.
Also, a larger mixed crystal ratio of Al, for example, AlInP is desired to be used in the current blocking layer for provision of light shutting-in function without light absorption. There is another problem in that the degree of freedom in designing of the semiconductor laser is restricted, because better crystal of the AlGaInP to be re-grown cannot be obtained on it where the mixed crystal ratio of the Al is big as shown in Table 2 to be described later.